1. Field of the Invention
The present invention relates to a cylindrical lens that is used in, e.g., an image forming apparatus, and linearly images a laser beam originating from a laser light source, and an optical scanning device that uses the cylindrical lens and images a laser beam, deflected by a deflection means, onto a surface to be scanned via an imaging lens.
2. Related Background Art
In a conventional optical scanning device used in an image forming apparatus, such as a laser printer or the like, as shown in, e.g., FIG. 1, a laser unit 2 is fixed to a predetermined position of an optical frame 1. A laser beam L coming from the laser unit 2 is linearly focused by a cylindrical lens 3, is deflected by a polygonal mirror 4, which is rotated by the drive force of a drive motor 5, and forms a beam spot on a surface 8 to be scanned of a photosensitive body via imaging lenses 6 and 7.
As shown in FIG. 2, the cylindrical lens 3 has an integrated structure obtained by adhering a first lens 3a having a positive refractive power, and a second lens 3b having a negative refractive power, to each other. When the cylindrical lens 3 is fixed to the optical frame 1, an adhesive 9 is interposed between the optical frame 1 and cylindrical lens 3, the position of the cylindrical lens 3 is adjusted to form a desired spot shape on the surface 8 to be scanned, and the lens 3 is then fixed.
However, the cylindrical lens 3 is adjusted before the adhesive 9 is set. During the adjustment, the adhesive 9 may enter the effective portion from a gap 3c between the first and second lenses 3a and 3b. For this reason, in the conventional optical scanning device, the adhesive that has entered the effective portion of the cylindrical lens 3 intercepts, refracts, and scatters the laser beam, and the spot image on the surface 8 to be scanned may deform. When such optical scanning device is used in the image forming apparatus, the image quality deteriorates.